This invention relates to an IP telephone set, an IP telephone system having the IP telephone set, and a dialing method in the IP telephone set.
JP-A-2005-26898 (Patent Document 1) discloses an emergency connection system. As briefly stated in the abstract of the above-referenced publication, in the emergency connection system, an IP (Internet Protocol) telephone set is connected, in a normal mode, to an IP network to perform telephone communication as an extension telephone set under control of an IP-PBX (Internet Protocol-Private Branch eXchange). If a failure occurs on the IP network or a power supply is disconnected or interrupted due to power failure or the like, the IP telephone set is connected to a general public network via a gateway to perform telephone communication as an outside line telephone set.